A condition that is becoming increasingly significant in medicine and epidemiologically and is affecting an ever greater proportion of the population, currently some 4%, is atrial fibrillation. In patients suffering from atrial fibrillation, disruptive pulses originating from the lung veins (pulmonary veins) pass into the cardiac conduction system of the heart, causing the patient's heart to beat only irregularly or very rapidly. A usual method of interventional therapy of atrial fibrillation is the electrical isolation of the lung veins. Catheters are introduced into the left atrium and the tissue in the area of the pulmonary veins, from which the disruptive signals originate, is ablated. This ablation is on the one hand attempted with conventional radio-frequency catheters (RF catheters). RF catheters make small punctilinear lesions (appr. 4 mm×4 mm). Isolating pulmonary veins with this technique over a large-surface area necessitates many working steps and a large amount of time. A new development in the area of catheter technology is so-called single-shot devices which are able, because of their larger size to ablate large areas of tissue in a single application. A preferred case involves what is known as a cryoballoon, as is offered for example under the name Arctic Front Cryoballoon®, by Medtronic CryoCath, PointeClaire, Quebec, Canada, which is placed in the area of the lung veins to be ablated and then cooled to a temperature of around −40° to −50° Celsius. Further examples for single-shot devices are the laser balloon, e.g. from CardioFocus, Marlborough, Mass., USA, or the PVAC multi-electrode catheter from Medtronic Ablation Frontiers, Carlsbad, Calif., USA. The now withdrawn “High-Intensity Focused Ultrasound (HIFU)” catheter of ProRhythm, Inc., Ronkonkoma, N.Y., USA also falls into the category of single-shot devices.
A prerequisite for successful use of single-shot devices, such as the cryoballoon for example, is generally good contact between catheter surface and heart tissue, since only in this way may energy, e.g. in the form of heat or cold, be transmitted in a sufficient quantity and the tissue ablated thereby, i.e. explicitly permanently destroyed. Devices must additionally often be placed in a precisely defined anatomical area to make effective and safe ablation possible. The cryoballoon must for example be placed in the antrum of the left atrium. Energy emissions in the incorrect areas are not effective and even dangerous, e.g. when they occur within a pulmonary vein. The anatomical configuration of the lung veins and of the left atrium is complex to an especially great extent and inter-individually very variable, so that single-shot devices such as cryoballoons for example cannot be used for each patient with a sufficiently accurate fit. If single-shot devices can be used with an accurate fit this as a rule brings about a very much faster and safer isolation of the lung veins by comparison with use of an RF catheter.
A decisive question before beginning the procedure is whether a single-shot device, e.g. a cryoballoon, can be used or whether there must be recourse to a conventional RF catheter. Clinical practice shows for example that a cryoballoon can achieve a very good ablation with non-selective patient quality in 25% of cases; in 75% of cases a supplementary ablation with RF catheters must take place after the cryoprocedure.
A widely-used method is to be presented here by way of example for use of a cryoballoon as a single-shot device for pulmonary vein isolation in the left atrium. In other single-shot devices the method is generally similar. With device-dependent details there can however be deviations. Currently for use of a cryoballoon a decision is made before the beginning of the procedure about the possibility of using it based on 3D imaging acquired beforehand. The suitable balloon diameter is determined with available 3D data by means of dimensioning in the slice images of these preoperative datasets. Under some circumstances this is also undertaken in a 3D view of a segmented left atrium. If only a two-dimensional measurement is to be able to be undertaken, there is the danger of inaccuracies. The measurement of all conceivable balloon positions in the antrum area of all four lung veins would be associated with a disproportionately high time outlay.
Whether the choice of balloon size was correct and whether it could be correctly placed can be checked in fluoroscopy by means of contrast means injection or Doppler ultrasound. Laser balloons which are equipped with an endoscope allow an optical check as to whether they are in good contact or not. These examples show that the check can however as a rule not take place until during the interventional procedure. If the choice of ablation instrument was not optimal however or if the ablation instrument could not be correctly placed, further measures which can impose strain on the patient and mean additional outlay in terms of time and money are necessary.